Memory devices are electronic devices arranged to store data. Memory elements can be combined in various arrangements in order to store multiple bits arranged in words or other combinations. Various electronic circuits, including semiconductor devices, such as, transistors are used as memory elements.
Memory elements may be classified in two main categories: volatile and nonvolatile. Volatile memory loses any data as soon as the system is turned off, thus, it requires constant power to remain viable. Most types of random access memories (RAM) fall into this category. Non-volatile memory does not lose its data when the system or device is turned off.
Demand for embedded nonvolatile memory (NVM) in integrated circuits has grown steadily over the past decade. Desirable characteristics of embedded NVM include low cost, low power, high speed, and high reliability (data retention and program/erase cycling endurance). NVM may be embedded in various integrated circuit (IC) technologies, for example, in the widely used Complementary Metal Oxide Semiconductor (CMOS) technology.
NVM is used to store serial number information, security information, settings, parameters, computer instructions (firmware), and the like. Radio Frequency IDentification (RFID) tags are an important field of application for reprogrammable NVMs since they store information inexpensively and reliably.
As NVM is pushed to the limit of its performance, problems emerge. These include data retention, program endurance, and write disturb. Often a memory has various portions that are used for different purposes. There typically is a portion for code storage where the content is changed very infrequently. There is also typically a user memory portion where the content is changed more often. In some instances, this was addressed by having two separate NVM arrays, each independently controlled, with different characteristics. This did not work, however, where silicon real estate was preciously low, such as in RFID tags. There, there are sections for storing such info as fabrication specific information, Electronic Article Surveillance (EAS), and Tag IDentification (TID) information that do not change or change infrequently. There are also sections i.e. user memory and memory for EPC segments that might be changed frequently. These, however, a single array is used because of space and power constraints.
The disclosure addresses this shortcoming of prior art by introducing a novel memory circuit architecture. The memory circuit architecture partitions a memory array into sub-arrays to take advantage of different memory use models.